package org.apache.lucene.store;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * A memory-resident {@link IndexOutput} implementation.
 *
 * @lucene.internal
 */
public class RAMOutputStream extends IndexOutput {
    static final int BUFFER_SIZE = 1024;

    private RAMFile file;

    private byte[] currentBuffer;
    private int currentBufferIndex;

    private int bufferPosition;
    private long bufferStart;
    private int bufferLength;

    /** Construct an empty output buffer. */
    public RAMOutputStream() {
        this(new RAMFile());
    }

    public RAMOutputStream(RAMFile f) {
        file = f;

        // make sure that we switch to the
        // first needed buffer lazily
        currentBufferIndex = -1;
        currentBuffer = null;
    }

    /** Copy the current contents of this buffer to the named output. */
    public void writeTo(IndexOutput out) throws IOException {
        flush();
        final long end = file.length;
        long pos = 0;
        int buffer = 0;
        while (pos < end) {
            int length = BUFFER_SIZE;
            long nextPos = pos + length;
            if (nextPos > end) { // at the last buffer
                length = (int) (end - pos);
            }
            out.writeBytes(file.getBuffer(buffer++), length);
            pos = nextPos;
        }
    }

    /** Resets this to an empty file. */
    public void reset() {
        currentBuffer = null;
        currentBufferIndex = -1;
        bufferPosition = 0;
        bufferStart = 0;
        bufferLength = 0;
        file.setLength(0);
    }

    @Override
    public void close() throws IOException {
        flush();
    }

    @Override
    public void seek(long pos) throws IOException {
        // set the file length in case we seek back
        // and flush() has not been called yet
        setFileLength();
        if (pos < bufferStart || pos >= bufferStart + bufferLength) {
            currentBufferIndex = (int) (pos / BUFFER_SIZE);
            switchCurrentBuffer();
        }

        bufferPosition = (int) (pos % BUFFER_SIZE);
    }

    @Override
    public long length() {
        return file.length;
    }

    @Override
    public void writeByte(byte b) throws IOException {
        if (bufferPosition == bufferLength) {
            currentBufferIndex++;
            switchCurrentBuffer();
        }
        currentBuffer[bufferPosition++] = b;
    }

    @Override
    public void writeBytes(byte[] b, int offset, int len) throws IOException {
        assert b != null;
        while (len > 0) {
            if (bufferPosition == bufferLength) {
                currentBufferIndex++;
                switchCurrentBuffer();
            }

            int remainInBuffer = currentBuffer.length - bufferPosition;
            int bytesToCopy = len < remainInBuffer ? len : remainInBuffer;
            System.arraycopy(b, offset, currentBuffer, bufferPosition, bytesToCopy);
            offset += bytesToCopy;
            len -= bytesToCopy;
            bufferPosition += bytesToCopy;
        }
    }

    private final void switchCurrentBuffer() throws IOException {
        if (currentBufferIndex == file.numBuffers()) {
            currentBuffer = file.addBuffer(BUFFER_SIZE);
        } else {
            currentBuffer = file.getBuffer(currentBufferIndex);
        }
        bufferPosition = 0;
        bufferStart = (long) BUFFER_SIZE * (long) currentBufferIndex;
        bufferLength = currentBuffer.length;
    }

    private void setFileLength() {
        long pointer = bufferStart + bufferPosition;
        if (pointer > file.length) {
            file.setLength(pointer);
        }
    }

    @Override
    public void flush() throws IOException {
        file.setLastModified(System.currentTimeMillis());
        setFileLength();
    }

    @Override
    public long getFilePointer() {
        return currentBufferIndex < 0 ? 0 : bufferStart + bufferPosition;
    }

    /** Returns byte usage of all buffers. */
    public long sizeInBytes() {
        return file.numBuffers() * BUFFER_SIZE;
    }

    @Override
    public void copyBytes(DataInput input, long numBytes) throws IOException {
        assert numBytes >= 0 : "numBytes=" + numBytes;

        while (numBytes > 0) {
            if (bufferPosition == bufferLength) {
                currentBufferIndex++;
                switchCurrentBuffer();
            }

            int toCopy = currentBuffer.length - bufferPosition;
            if (numBytes < toCopy) {
                toCopy = (int) numBytes;
            }
            input.readBytes(currentBuffer, bufferPosition, toCopy, false);
            numBytes -= toCopy;
            bufferPosition += toCopy;
        }

    }

}
